Lady Ironbeard not doing triple damage

Periodically (maybe 2-3% of the time) Lady Ironbeard is not doing triple damage when she has greater armor than her target. I wonder if anyone else is experiencing this? Really frustrating when you are counting on that extra damage. Unfortunately I don’t have a way to reproduce the bug. Several times it happened when the enemy target was stunned, but now I think that was irrelevant since today it happened to an unstunned valkyrie.